The size and weight of cone loudspeakers can be a bottleneck for thin, light electronics. Loudspeakers that rely on the bending motion of a stiff plate to produce acoustic radiation have been proposed as an alternative to traditional designs for nearly a century. A plate whose vibration is actuated by an electromagnetic coil driver or piezoelectric bending device, known as a “Distributed” or “Diffuse” Mode Loudspeaker (DML) because of the way it vibrates in complex combinations of resonant modes, can have some promising acoustic characteristics. However, it has not become as widespread as the ubiquitous cone loudspeaker. Despite the fact that thin, lightweight plates have the potential to be integrated into many more spaces than heavy, bulky cone loudspeakers, they can suffer from weak and reverberant bass response and may be regarded as poor for hi-fidelity audio applications.
An investigation of mechanical impedance matching between drivers and plates and plate radiation efficiency and plate frequency response characteristics can show that plates can be suitable for use as a source of audio reproduction. Plates can have relatively omnidirectional radiation patterns over the audio band due to their complex and spatially complex vibrational characteristics. However, plate loudspeakers can suffer from temporal (equivalently phase) distortions caused by the spread of initially localized driving forces across the entire surface of the plate, since construction can involve the use of a single small driver to actuate the panel. Temporal distortion has been shown to affect hi-fidelity audio reproduction, especially in speech applications. The temporal response issues can distort high amplitude transients in music and speech when plates ring at their resonant frequencies. Moreover, the Speech Transmission Index of a traditional single driver DML can be considerably lower than that of traditional loudspeakers, which can make them less ideal for critical audio reproduction.
The weak bass and reverberation effects can be somewhat compensated for by using equalization and digital inverse filters. However, the spatial diffusion properties mentioned earlier can cause inverse filtering to work only at select spatial points in the radiation zone of the plate, a result which may mean little for loudspeakers meant to reproduce audio over a large area. Materials with high internal damping, meant to decrease reverberation, also can have the effect of causing weak bass response.
Therefore, what are needed are devices, systems and methods that overcome challenges in the present art, some of which are described above.